1. Field of the Invention
The invention is in the field of fabrication of thin walled objects, such as infrared absorbent cold shields for infrared cameras and sensors.
2. Background Art
Deposition processes have been used in the past to produce self supporting objects. Mattia (U.S. Pat. No. 3,457,157, issued Jul. 22, 1969) discloses an apparatus for producing tubing of various cross section shapes by an electroforming process. Conn, et al. (U.S. Pat. No. 3,939,046, issued Feb. 17, 1976) disclose a method of electroforming a thin metal foil with a desired raised pattern by coating a thin metal layer on a master substrate embossed with the desired pattern. The master is made of one material, such as aluminum, and the deposited layer is of another material, such as nickel, that is not soluble in a liquid that will dissolve the master material. The master is dissolved, leaving a patterned foil. The use of multilayer platings to achieve particular mechanical properties is disclosed. Kelly, et. al. (U.S. Pat. No. 3,187,639, issued Jun. 8, 1965 and by Hurwitz, et.al. (U.S. Pat. No. 4,300,959, issued Nov. 17, 1981).
Deposition methods, materials, and solutions for electroplating and other forms of film deposition, such as electroless plating, evaporation coating, sputtering, and reactive sputtering are widely known, since surface layer deposition for many applications is a important industrial process. A review article of particular interest in connection with the herein disclosed invention is "A Survey of Electroforming for Fabricating Structures", W. H. Safranek, Plating, Vol. 53, No. 10, Pp. 1211-1216 (October 1966). This article details many uses for thin wall electroformed structures and the materials, solutions, and plating conditions used and the range of variation of these quantities to produce layers with different properties. The disclosure of this article is incorporated herein. There are similar extensive literatures in other coating fields.
The use of electroforming to produce an infrared absorbing cold shield is disclosed by DuPree, et. al. in U.S. Pat. No. 5,196,106. DuPree's invention lies in the provision of a layer of infrared absorbing material on the interior surface of the electroformed shell. Such cold shields are used to surround the detection element of an infrared camera and shield the element from any infrared radiation outside of a prescribed cone of radiation entering through an aperture at the top of the shield. Radiation entering the aperture at larger angles strikes the inside shield wall. DuPree's interior coating is intended to absorb such unwanted radiation and prevent its reflection onto the detection element. Another approach to capturing infrared radiation entering the aperture outside of the prescribed cone of angles and to more precisely define the acceptance cone is to provide the shield with a series of internal baffles. However, the fabrication of shield with internal baffles has, heretofore, required costly assembly steps and use of adhesives that can produce outgassing and contamination in the low temperature and high vacuum environments in which these devices are often used. Such assembled structures are also susceptible to mechanical failure at the joints between the shell and baffles and to assembly errors.